In telecommunications, specific frequencies or ranges of frequencies can be allocated for use by broadcasting services in different geographical areas. Such ranges of frequencies are often allocated by international agreement or a governing body. For example, the television channel 2 in North America references the broadcast band of frequencies between 54 and 60 MHz.
The electromagnetic spectrum that mobile computing devices use for wireless communication is treated as a limited resource. Governments control where in the spectrum particular wireless technologies can operate, and also control what entities can use particular portions of the spectrum (e.g., through high-cost spectrum auctions). Because a particular entity will thus have limited spectrum and will have paid a large amount for it, various mechanisms are used to maximize the data that a network of mobile computing devices and corresponding base stations can exchange in a particular portion of spectrum.
Some frequency ranges are not allocated by governments to a specific entity, and can be used by the public or designated entities as long as no other transmissions are being broadcast over the frequency ranges by other devices. Similarly, some frequency ranges are assigned to specific entities, but are not in use at a particular location. For example, frequencies that are assigned to an otherwise active radio frequency channel may not serve to transmit data, but may serve as a guard band between other channels. These inactive radio frequency ranges can be made available for use by communication devices. As such, some frequencies or bands of frequencies are not being used at a particular location, or have recently become available for use as broadcasters that have switched from analog transmissions to digital transmissions.
Spatial division multiple access (SDMA) is a mechanism that is used to increase the amount of data exchanged in a wireless network. In SDMA systems, users are multiplexed in the spatial domain so that multiple users can broadcast and receive from different spatial degrees of freedom. For example, several mobile computing devices can communicate with the same base station at the same time and over the same band of frequencies if the devices are geographically separated (i.e., if the devices are located in different spatial degrees of freedom). As one example, two simultaneously-communicating devices may be located on opposite sides of a broadcast and reception tower of a base station. SDMA can be achieved in a network by using an array of antennas that can adapt signals that radiate from a base station in the direction of a client device (e.g., using transmit and receive beamformers). Additionally, an SDMA system can be configured and deployed for time division multiple access (TDMA), by which multiple client devices that are geographically located near each other can share the same spatial-frequency resource by having each device transmit or receive only during certain slices of time that are coordinated with each other.
Modern wireless data communication systems provide bandwidth for use by rich computing applications on mobile devices. For example, users of wireless devices such as smart phones can make telephone calls, receive emails, and even receive full motion audio/video broadcasts on their mobile devices. Every time a great new service is offered, users of wireless devices consume data associated with the service, requiring more and more bandwidth. As a result, the airwaves are filled with data going to and from an increasing number of wireless computing devices that each require growing amounts of data.